Applications based on detections and communications by radiofrequency or hyper frequency waves require the capability to process electromagnetic signals that have significant dynamics. Examples of such applications are systems receiving electromagnetic waves, such as radiofrequency stations and radar wave receivers.
The dynamics of the signals are increasingly significant in increasingly dense electromagnetic environments in which the signals overlap in time. In this situation, signal processing subsystems can be saturated by powers received by an antenna system.
For example, in receiver stations with frequency modulation, there is a threshold beyond which a received signal is no longer usable.
A signal power limiter device is generally used before signal amplifiers in a received signal processing subsystem. A power limiter device can conventionally be produced from an assembly of semiconductor diodes. Such a limiter device may be effective for protecting sensitive electronic circuits situated downstream of the limiter in a digital signal processing subsystem. However, such a limiter has the major drawback of distorting the signals to the point that they can no longer be used by the digital processing subsystems. In particular, the phase of the attenuated signals is not retained. Furthermore, the goniometry and/or signal source locating processing operations then become inoperative. Such locating processing operations are notably used by new generation base stations in radiocommunication systems.
New generations of wireless communication terminals are therefore faced with increasingly difficult problems associated with three types of antinomic constraints:                the first constraint is to detect, recognize and use signals that are increasingly varied in terms of power and frequency, notably for all types of emissions, in all the wavelength bands, for the most diverse radiocommunication sets, from tactical sets to portable telephones, and do so over a very wide band spanning a few hundreds of megahertz to several gigahertz;        a second constraint is to be protected against signal interferences, the peak power of which will increase in time given the current technical developments;        a third constraint is to accurately locate in space, to within a fraction of a degree for example, all the sources emitting electromagnetic signals by wide band interferometry techniques. A saturation of the receiving subsystems leads to a loss of the signals, in which case a processing of the signal phases is pointless. It is therefore useful to have a function that allows a phase measurement while the various signals are being received. This type of function does not currently exist, notably because the receivers are sensitive to saturation, even when they are protected by current power limiting devices.        
One function of a limiter, placed immediately after a receiving antenna, is notably to avoid saturation or disabling, potentially to the point of destruction, of the sensitive elements situated downstream of the signal processing subsystem, and in particular of an amplification subsystem with low power level.
The objective of a signal power limiter is notably to satisfy the following specifications:                a first specification may be a resistance of the limiter to high received signal powers, for example between a few hundred milli-watts and a few hundred watts, and possibly up to a few kilowatts, and for one and the same limiter device;        a second specification may be a response time that is as short as possible, of the order of a nanosecond, in order to protect sensitive stages of the signal processing devices and do so from the rising edge of the incident power signal;        a third specification may be to have the lowest possible insertion losses, less than 1 dB for example, between a receiving antenna and a low noise amplification stage of the signal processing device;        a fourth specification may be an integration of the limiter in a small volume: this notably raises an issue of high dissipated power in a very small volume;        a fifth specification may be the possibility of dynamically adjusting the thresholds so as to be able to continue to use, as much as possible, attenuated and deformed signals that have passed through the structure of the limiter.These major specifications may be complemented with a sixth specification, which is the possibility of performing radio-goniometric operations, such as locating the direction of an electromagnetic emission even in the presence of high power interference.        
Current limiters are mainly based on a partial dissipation and a reflection of a portion of the incident signal by discrete semiconductor diodes, such as Schottky diodes or PIN diodes. The PIN diodes are PN junction diodes with intrinsic region. The Schottky diodes or PIN diodes are inserted at points located on a transmission line. The materials most commonly used for the diodes are, for example, silicon, gallium arsenide, or even gallium nitride.
Although very commonly used, the current limiters have a major drawback: their poor performance levels in the hyper frequency domain. In practice, the insertion losses of the current limiters are high, notably greater than 1 dB. Such insertion losses are not optimal for certain specific applications in which the signals are very low in amplitude. For low amplitude signals, it is essential to minimize the insertion losses, such as in radars for example. Furthermore, a signal distortion induced by the diodes used in the current limiters is a nuisance for applications that require their components to be greatly linear notably to avoid intermodulation phenomena between multiple signals.
Furthermore, the resistance of the current limiters in terms of received power is limited to a few tens of watts. Overheating induced by the passage of the current during incident signal power limiting phases may lead to destruction of the components situated downstream of a current limiter.
Other solutions based on superconductive lines also exist, but can be used only in environments cooled to very low temperatures. Such solutions are therefore difficult to integrate with other technologies.
Solutions based on ferroelectric and magnetic materials may be envisaged but cannot be fabricated inexpensively by collective methods. Furthermore, their performance levels in the hyper frequency domain and their power resistance over time remain uncertain.
Similarly, solutions based on ferrites or plasma lines have been published, and some are used in specific equipment, such as nuclear instrumentation for example, but, generally, they meet only one of the limiter specifications well, and meet the others unsatisfactorily.
The current solutions therefore do not meet the necessary specifications for a limiter.